CHROMagar™ orientation urine culture medium produces matrix-assisted laser desorption ionization-time-of-flight mass spectrometry spectra misidentified as Mycoplasma arginini and Mycoplasma alkalescens.

Matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry is commonly used to identify bacteria and yeasts. Studies indicate that MALDI-TOF is relatively indifferent to the medium used for culture. We report on an investigation into high- and low-confidence MALDI-TOF misidentifications of Mycoplasma arginini and Mycoplasma alkalescens from urine specimens plated to CHROMagar™ Orientation medium that appear to be due to the intrinsic mass spectrum of the medium.